1. Field of the Invention
This invention relates to a coating composition which is capable of yielding a hard coating film having a high refractive index and a very high hardness. The invention also relates to coated articles obtained by coating and cuing the composition on appropriate substrates.
2. Description of the Prior Art
Plastic lenses, which are a kind of transparent shaped article, are better in safety, ease of processability, fashionability and lightness than glass lenses. Recent developments of hard coat techniques and reflection inhibiting techniques for the lenses have expedited the rapid spread of the lenses. The silica-based hard coat film which is applied to plastic lenses has attracted attention due to its high hardness and high scratch resistance. Nevertheless, as plastic lenses having a high refractive index have been developed and start to be in wide spread use, there appears a phenomenon where interference fringes are developed owing to the great difference in refractive index and also in thickness between the hard coat film and the plastic lens substrate.
Using, in place of silica, high refractive index metal oxides such as antimony oxide, zirconium oxide, titanium oxide, tin oxide and the like, attempts and developments have been made to form high refractive index coating films on plastic lenses and other transparent moldings or shaped articles.
For instance, Japanese Patent Publication No. 63-37142 discloses a hard coating film comprised of antimony oxide and an epoxysilane, and Japanese Laid-open Patent Application No. 5-2102 discloses a hard coating film comprised of fine particles of titanium oxide, iron oxide and silicon dioxide and an epoxysilane. Moreover, Japanese Laid-open Patent Application. No. 5-164902 discloses a hard coating film which is made of fine particles of titanium oxide, cerium oxide and silicon oxide, an epoxysilane and a tetrafunctional silane compound.
However, the existing high refractive index hard coating films on transparent substrates have been able to undergo little dyeing after coating or may be dyed in a slight degree but cannot be subjected to deep color dyeing. For deep color dyeing, it is necessary to lower the hardness of the hard coating film.